1. Field of the Invention
The present invention relates to an illumination light quantity setting method in an image measuring instrument, and particularly to an illumination light quantity setting method in an image measuring instrument including an image pickup for imaging a plurality of measured points based on a preset measuring procedure and an illuminator for irradiating the measured points to measure a dimension and a shape of an object to be measured.
2. Description of Related Art
A conventional image measuring instrument has been used to measure a surface texture of an object to be measured by applying an image processing to an image of the object to be measured, the image being captured by an image pickup. It is important for the image measuring instrument that an illumination condition (an illumination preset value) is set to enhance contrast of the captured image so that an edge position of the object to be measured is reliably and accurately detected.
In such image measuring instrument, a system for optimally setting an illumination condition when detecting an edge position has been known (for example, see Document 1: JP-A-09-304034 (FIG. 3)).
In the image measuring instrument disclosed in Document 1, light quantity is initially changed by several pitches at every predetermined measured point in order to preliminarily set optimal light quantity at the measured point, and then a contrast value on an image at the measured point is calculated at every change of light quantity. Subsequently, an illumination light quantity having the highest contrast value is calculated as an illumination preset value by applying the contrast value and illumination light quantity to a quadratic function. The calculated illumination preset value is set for every measured point to be stored in a work memory or the like.
The image measuring instrument images the plurality of measured points with light having illumination quantity of the optimal illumination preset value with reference to the stored illumination preset values. The image measuring instrument stores a part program that sequentially measures the plurality of measured points in accordance with a preset measuring procedure. By executing the part program, a plurality of objects to be measured having the same shape can be efficiently and repeatedly measured.
However, in the image measuring instrument disclosed in Document 1, when actual quantity of light irradiated from an illumination light source is changed, such as when the illumination light source (illuminator) deteriorates with the passage of time or when the illumination light source is replaced, it is necessary that the illumination preset values in the part program are modified for all of the measured points. This modification has been effort-consuming.